This invention relates to smoking articles which produce substantially no visible sidestream smoke. More particularly, this invention relates to a smoking article in which the sensations associated with the smoking of tobacco are achieved without the burning of tobacco.
A substantial number of previous attempts have been made to produce a smoking article which produces an aerosol or vapor for inhalation, rather than conventional tobacco smoke. For example, Siegel U.S. Pat. No. 2,907,686 shows a smoking article consisting of a charcoal rod and a separate carrier impregnated with flavorants and a synthetic "smoke" forming agent which is heated by the burning charcoal rod. The charcoal rod is coated with a concentrated sugar solution so as to form an impervious layer during burning. It was thought that this layer would contain the gases formed during smoking and concentrate the heat thus formed.
Another smoking article, shown in Ellis et al. U.S. Pat. No. 3,258,015, employs burning tobacco in the form of a conventional cigarette to heat a metallic cylinder containing a source of nicotine, such as reconstituted tobacco or tobacco extract. During smoking, the vapors released from the material inside the metal tube mix with air inhaled through an open end of the tube which runs to the burning end of the smoking article. Ellis et al. U.S. Pat. No. 3,356,094 shows a similar smoking article in which the tube becomes frangible upon heating, so that it would break off and not protrude when the surrounding tobacco had burned away.
Published European patent application No. 0 177 355 by Hearn et al. shows a smoking article which produces a nicotine-containing aerosol by heating, but not burning, a flavor generator. The flavor generator could be fabricated from a substrate material such as almumina, natural clays and the like, or tobacco filler. The flavor generator is impregnated with thermally releasable flavorants, including nicotine, glycerol, menthol and the like. Heating of the flavor generator is provided by hot gases formed as a result of the combustion of a fuel rod of pyrolized tobacco or other carbonaceous material.
Banerjee et al. U.S. Pat. No. 4,714,082 shows a variation of the Hearn et al. article which employs a short fuel element. The performance of the article is said to be improved by maximizing heat transfer between the fuel element and the aerosol generator. This is effected by preventing heat loss by insulation, and by enhancing heat transfer between the burning fuel and the flavor generator by a metallic conductor. A spun glass fiber insulator surrounds the fuel element and aerosol generator assembly.
The Banerjee et al. device suffers from a number of drawbacks. First, the resilient glass fiber insulating jacket is difficult to handle on modern mass production machinery. Second, the glass fibers may become dislodged during shipping and migrate through the pack to rest on the mouth end of the article, giving rise to the potential for the inhalation of glass fibers into the smoker's mouth. Additionally, the use of a metallic heat conductor may be somewhat inefficient because the conductor itself absorbs much of the heat produced by the fuel element.
It would be desirable to be able to provide a smoking article in which a flavored aerosol releasing material is efficiently heated by hot gases formed by the passage of air through, and by radiation from, a carbonaceous heat source.
It further would be desirable to avoid the potential for inhalation of glass fibers by a smoker of such an article.
It still further would be desirable to provide such an article which has both the look and feel of a conventional cigarette.